Reproducing and recording of sound



May 7, 1929. A. F. SYKES REPRGDUCING AND RECORDING OF souun 5 Sheets-Sheet 1 Filed Nov. 16- 1920 May 7, 1929. A. F. SYKES REPRGDUCING AND RECORDING OF SOUND Filed Nov. 161 1920 5 Sheets-Sheet 2 y 7, 1929- A. F. SYKES 1,711,551

REPRODUCING AND RECORDING OF SOUND Filed-Nov. 16. 1920 '5 Sheets-Sheet 3 May 7, 1929. I SYKES 1,711,551

REPRODUCING AND RECORDING OF SOUND Filed Nov. 16- 1920 5 Sheets-Sheet 4 y 7, 1929- A. F. SYKES 1,711,551

REPRODUCING AND RECORDING 01 SOUND f Filed Nov. 16.1 5 Sheets-Sheet -5 Patented May 7, 1929.

UNITED STATES ADRIAN FRANCIS SY KES, OF NEW BARNET, ENGLAND.

REPRODUCING AND RECORDING- 05 SOUND.

bpplicatiomfiled November 16, 1920, Serial No. 424,421, and in Great Britain November 18, 1919.

Thisinvention relates to apparatus for the .conversion of sound into equivalent variation of electric currents or potentials and to the conversion of electric currents or derivatives thereof into mechanical vibration for the purpose of reproduction. I

The primar object of my invention is the production of phonograph or gramophone records of improved fidelity in-which tonal purity, definition and beauty are enhanced while disturbances, false tones and blasts are minimized and in general in which defects usually attributed tothe natural tones of diaphragms and the resistance of. the wax to impression are eliminated.

In the-full practice of my invention I employ a primary detector of a non-resonant nature which serves to derive electric potentials from sound waves, a system for modifying or distorting the Wave forms of the po-' I way are distorted by means of the thermionic It will be convenient to deal with the problem of the derivation of electric currents e'qui-.

valentto sound waveslor systematically differing therefrom and the problem of engraving mechanical equivalents of electrical oscillations or systematic derivatives thereof separately and then to make some remarks on their use in combination.

Thus as regards detection my invention consists inlallowing sound to vibrate a plain mass freely supported; to the mass is rigidly attached an electricalconductor immersed in sult is a practically true replica of the wave of excess pressure.

I will now define what I mean by a plain mass. Consider a body of mass M to be acted upon by a force which causes it to vibrate in simple harmonic fashion, then if s=amplitude of vibration a= acceleration t=time 7 frequency the expression for the acceleration is d s a W 41r f 8 I define a plain mass asa body so supported and free from external or internal constraint that it would require a force of M times 411' f 8 to cause it to execute this vibration. A

diaphragm of mass M does not in general for the purpose of this specification constitute a plain mass since any tones it possesses require much less force of the same frequency or nearly the same frequency to excite to a given amplitude than corresponds to'the above formula. For the purpose of this specification the reaction of the supports necessary to maintain the mass in position relative to the other apparatus is neglected since the constraint is trivial compared with the inertia of the mass itself. A plain mass hasnow been described technically; it-will be observed thatit does not reclude a-oomposite nature for the body emp oyed. I v

' Mathematically if the mass is acted upon by the pulsatory force of sound the amplitude of vibration to each harmonic is inversely proportional to the square of the frequency of the particulariharmonic, and the maximum veloc- ,ity attained is inversely proportional to the v frequency, hence the E. M. F. enerated in the coil falls uniformly as the loo equency rises.

If now this E. M.-F. is applied to anapparatus capable of enlarging every harmonic in I something between the two occurs.

ics referred to are harmonics of pressure on the body. At this stage it may be observed that without any modification the coil generates true electrical equivalents of the 01'- dinate of particle displacement.

Preferably the detector so defined is modified so that although the actual body vibrated may not in fact be free from mechanical tones in effect it behaves as though it were. Thus the coil is no longer attached to a heavy inert body but instead is wound pancake fashion, that is a-single or multi-layer spiral, the turns of which are bonded together with gum, shellac, or other bin-ding material. With advantage the magnetic air gap can be made large and might be six centimeters or even more. The coil is either hung in the gap or fastened across it by tissue paper or other tenuous membrane. Two definite conditions arise and an intermediate stage. In the first place if the weight of the coil is so great that next to no sound is transmitted by it to the air beyond, the voltage generated is the equivalent of the displacement curve; in the second place if the coil is so tenuous, it might be composed of gold leaf, that it does not sensibly obstruct the sound the excess pressure wave is reproduced; in the third place if the coil is of intermediate weight then for high frequencies the displacement wave is represented, for low frequencies the excess pressure wave is represented, while for intermediate frequeripies ny overtones in a coil used in this fashion must in the main be obliterated by the averaging process which takes place, that is why the coil actsas a body devoid of overtones and conforms to the idea of a plain mass.

An apparatus with the property of enlarging, every harmonic in proportion to its vfrequency, that is of obtaining the electrical equivalent of mathematical differentiation, can be constructed in the following fashiofi. Let the E. M. F. generated in the detector coil be applied to the grid of a thermionic valve, or any distortionless electric relay, and let a small inductance be placed in a plate circuit; then the potential developed on the inductance will be the differential of the grid voltage. Care would of course be taken to avoid the use of any iron core in such fashion as to distort the result by the influence of hysteresis or eddy currents. A device of this nature cannot be loaded or in other words cannot supply more than a trivial amount of current without vitiating the conditions; it is the e uivalent of a current transformer on open circuit and a valve'so used is one used meificlently or Wastefully 1n the amphfylng sense.

So much for the detection aspect of the subject. I now turn tothe converse, the derivation of mechanical vibration from electrical vibration or voice currents. The principles involved are very similar. I presume in the first place that true voice currents are/required to be represented by the displacement of a plain mass, an inert coil carrying a sapphire engaged with a wax surface of sufficient softness not materially to interfere with the vibration which would be induced in the mass in the absence of the wax. By wax is meant the usual composition employed in the production of master records.

The coil is simply floated on the wax surface for vertical or phonograph recording and suitable modifications are introduced to meet the needs of the lateral or gramophone cut. Such a coil when supplied with currents properly representing the voice, musical performance or telephone message it is desired to record does not vibrate in a manner truly cor.-

responding to theelectrical variations but on the contrary the wave form of the vibration tion is that the harmonics are magnifiedin the proportion of the square of the frequency" which change is brought'about by the use of condensers or inductances in the following fashion. Supposing the electrical variations available can supply no appreciable power they are in the first place magnified by athermionic valve relay or the like the last valve of which is fairly powerful. A small inductance is placed in the plate circuit of this latter valve and the variation of electrical potential on this inductance is the differential of'the current in the plate circuit so that every harmonic is exaggerated in proportion to its frequency. For this to be realized in practice the resistance of the plate circuit must be large compared with the impedance of the inductance used for the frequency considered. The potential across the inductance is now caused to operate a second valve also with a small in ductance in its plate circuit; the variation of potential on this second inductance is the. differential of the plate current and hence every harmonic is exaggerated inthe proportion of its frequency, so that the variations of poten tial on this second inductance referred to the signed to supply current to the recording coil. The term coil? is to be understood in a broad sense; it may not involve a complete turn if a current transformer is used. A Fessenden vibrator (described in Patent No. 1,167,366) might conceivably be adapted to the case.-

Among resistances that may be encountered in apparatus for recording'on wax, may be mentioned, firstly, a thrust from the wax varying with and for small displacements proportional to the departure from the mean ,-pos1t1on; secondly, a resistance of the nature of-viscosity, a resistance depending upon the velocity of the moving parts; thirdly, theinertia of the recording element itself. Of.

these resistances which comply with the conditions requisite for a damped tone, the first only modifies in scale the true voice current itself, the second can be corrected by an appropriate fraction of the differential of the voice current,-the third by the second dif-.

ferential of the voice current. In the practice of the invention, however, the inertia of the engraving element constitutes so largea proportion of the total resistance that for most purposes it is not necessary to make any provision for any other resistances. Nevbe incorporated in the system.

Just as in the case of the detector the recording coil behaves as a plain mass and not as a resonator as isthe' diaphragm of a telephone or the like. A vibrating element of erthelessif desired such compensation can this character is never used in practical telephony or sound recordlng for two reasons.

In the first place it is insensitive, and secondly it distorts the sound. By the use of relays of distortionless character now avail- I able the objection as to sensitiveness disappears; andby suitably modifying the Wave form of the currents before allowing them to vibrate the coil the distortion is eliminated.

The point of'viewadopted is that in all -cases the mass of, thedetectng orinscribing agency is compensated for completely regardless of the frequency; while elastic control or viscous damping are either, and preferably,

.made relatively negligible or are provided for by appropriate currents derived from the sound. Thus if the vnatural period of. the engraving instrument corresponds to 250 vibrations a second, and should that be the only period which can be readily excited by the electrical forces brought to bear, at a frequency of IQQO vibrations a second themas s,

is largely the predominant factor and set determines the extent of the vibration and the electrical forces are artificially distortedto ensure that the mass will vibrate overthc proper'range notwithstanding that the frequency is much above the natural frequency of the instrument. 'The principle for dealing \with any tone which, occurs'in' the apparatus onsists in reducingjthe"electrical forces at t ke resonance point'to the amount required so t overcome the dampin only.-

05 placement wave be available'and subject its Suppose a detector w ich derives current pr potential from the sound'equivalent to the excess pressure wave be available. Alternatively let a detector expressing the dispotential to a processof differentiation so as to derive a. -.result equivalent to the excess pressure wave. Let this detector control 'an amplifying valve in whose plate circuit is placed a large inductance in parallel with a,

combination of a small inductance, a condenser and aresistance, all in series, and so proportionedas to be the electrical equivalent of the mechanical vibrating system. By this I mean that the time period is the same and the damping of the same degree. The impedance of the electrical system must be sufiiciently small as to permit the changes in valve current to be driven through Without sensible modification. lVith this state of affalrs the potential across the combination is such as to'compensate for the mass, elasticity and damping of the mechanical system for any frequency up to that when the impedance of the electrical combination becomes comparable with the resistance of the valve itself. In'relation to the displacement wave of the sound the potential across the condenser, the resistance and the inductance respectively, is the-equivalent of the unaltered wave, the first differential and-the respectively.

The velocity attained by the mechanical system at any instant is the mechanical equivalent of the plate circuit current and hence the amplitude developedjis'the integral of that current with respect to time and there fore corresponds to the displacement curve of the sound. At the resonant frequency the voltage across the condenser is'equal and 0p posite to the voltage across; the inductancesecond 7 difl'erential and therefore the-'only potential supplied to reasons of stability considerable elastic controlmust be rovided otherwise the armature simply ies to the pole or poles. By taking into account this control such a device could be operated on the lines of my inven} tion. An example is furnished in Figure 11 of the drawings filedwith-this specification.

Possibly by -aireful experimental study of a reed-for diaphragm telephone receiver-such an instrument could be improved as a recorder bycompen'sating for each of its'tones so as to render the re'sonantaction more uniform.

The recordin element most avoured at the present time 1s a small compac coil weigh-- ing about 5 grammes adapted for torsional vibration located in a single magnetic air gap (induction density about 15000 c. g1 s. lines), that is, without iron armature. The coil is under weak elastic control purely for facilitating the use of a gravity method of determining the depth of cut in the wax. In place of the ordinary telephone currents providing a link between the detector-and the recorder it is obvious that the detector may control directly or indirectly a high frequency transmitting set similar to any used for wireless telephony and so modulate a carrier wave but inasmuch as the modulated carrier is rectified before operating the recorder and therefore becomes a telephone current no description of such matters is included in this specification. In fact the recorder could register messages or musical selections transmitted by wireless telephony from distant countries or from modulated carrier currents transmitted by means of wires. Apart from the subject matter of this invention, however, all such apparatus and schemes are dealt with in books on wireless telegraphy. I

I have now described both the detector and the recorder separately and I now turn to their use in combination. The standard of reference adopted has been the wave of excess pressure. Particle displacement as well as pressure difference over a small interval can be derived from the wave of excess pressure by a process of integration or differentiation as the case may be. The detector described with reference to Figure 2 takes'the excess pressure as the standard. It has been observed that if the process is stopped at the stage when the mass is exposed on one side only to the wave of excess pressure and simply carries a coil immersed in a magnetic field, then the E. M. F. induced is in terms of particle displacement. Recordings intermediate between that of full excess pressure and particle displacement can be obtained by the use of an inductance in one or other of the dis tortion circuits, which inductance tends more and more merely to check the current as the frequency rises and not to differentiate. These remarks are made because in making a record it may be necessary to take some account of the natfural characteristics of the machine on whichfit is intended to reproduce it. -My invention enables the operator to compensate for various influences which would otherwise impair the. fidelity of the reproduced sound. I

Of course if the characteristic of the detecting or reproducing agency supplies one or more of the steps required by my. system asdescribed then such step or steps would be omitted. In other words if it is not desired to record accurately the voice currents or potentials available but some modification thereof the invention is varied accordingly; in fact in the making of a sound record the effect obtained necessarily involves the combination of the detecting, engraving and reproducing instruments. In particular should the phonograph or gramophone tend to give undue prominence to a harmonic of a particular pitch such a harmonic could be taken account of in the recording by shunting one of the valve transformers with an oscillation circuit which at the particular frequency reduces the efliciency of transformation.

From the point of view of the deficiencies of a given sound reproducing machine or phonograph, the recording which in combi-A,

nation with the machine gives 'a faithful reproduction of the original sound may not itself represent anything very definite, which is really another way of saying that the art must remain experimental until standarized. Apart then from permitting an engraving to be made equivalent to, say, the displacement.

wave, that is, an engraving with a well understood meaning, the system provides scope for a wide range of tone control. Any derivative of the excess pressure wave either by integration or differentiation is theoretically obtainable and also intermediate stages.

Although I'have described recording apparatus using throughout the principle of the plain mass or non-resonant system cases may arise where the very great sensitiveness in-. herent in the combination of a microphone and sound concentrating trumpet presents great possibilities. By care and experiment such apparatus can be made to yield most useful results and in combination with a plain mass recorder as described such results can be engraved accurately on the wax.

' Similarly it may happen that it is desirable to use the detecting part of the invention in conjunction with any recording telephone.

My invention is illustrated by the accompanying drawings. Figure 1 is an elevation in part section of a non-resonant detector. Figure 2 is a fragmentary view in part scc tion of a non-resonant detectorand a diagram of connections. Figure 3 is a rear elevation of a non-resonant sound detecting element with attached coil. Figure 4 is a fragmentary sectional view of a non-resonant detector showing a variation in construction. Figure 5 is a side elevation of a non-resonant recorder with stationary armature. Figure 6 is a fragmentary view in part section of a non-resonant recorder with annular magnetic air gap. Figure 7 is an inverted plan of the apparatus illustrated in Figure 6. Figure 8 is adiagram of connections applicable to recording the vibration of a sensitive liquid jet. Figure 9 is a diagram indicating a method of making a disc record using a non-resonant electro magnetic detector and a non-resonant electro-magnetic recorder. Figure 10 is a fragmentary section of a detector with pancake coil of wire whic detector is in eifect non-resonant. Figure 11 is a diagram showing the invention applied to apparatus of the Bell telephone receiver class so as to convert it into a recording de vice which is in effect non-resonant. Figures 12, 13 and 14, illustrate recording apparatus with single magnetic air gap and gravity adjustment. Figure 12 is an, eleva- 4 cemented together; a former or frame 5*car- 7 recording telephone.

ries a coil of wire 6 immersed in the field between the poles 7, 8 and 9, of the electromagnet 10 with a winding 11. The plain mass 1 is supported by ligaments, light springs or the like, in an aperture in a Wall 12 shown in section from which it is separated by a space 13 usually made very small. To operate the appartus sound is produced on the side of the wall remote from the electromagnet. A convenient arrangement is to make the wall 12 a division between. two rooms, one the recording room and the other the instrument room. A horn or trumpet may-if desired be used to concentrate the soundwaves upon the mass 1.

Figure 2 is a fragmentary view in part sec-' tion of the elevation of Figure 1. The ligaments' 14 attached to pro ections 15 in they wall and plain mass respectively are shown supporting the mass. Terminals 16 receive wires from the coil 6. Across these terminals are placed a non-inductive resistance 17 and a-condenser 18. Between the terminals 19 is felt the voltage variation across the noninductive resistance 17. A number of valve relays in cascade are interposed between the terminals19 and the terminals 20- so that the plate current in thelast of the series is carried by the wires from the terminals 20 and this plate current is an enormous magnification and replica of the potential across the terminals 19; this plate current is caused directly or indirectly to operate a receiving or Figure3 is a view of the coil-6 wound on its former 5 at the rear of the plain mass 1.

' The poles 7 8 and 9, of the electromagnet are indicated by dotted lines. Of course the former and coils move with and therefore add to the mass of the primary detector 1.

Figure 4 is a modification of the apparatus represented in Figure 1'. Here thepoles 7 thepeg circles the and ring type, that is, the pole 7 en pole 8 and the field. is radial. In this construction the pole 7 is built into and forms part of the recording wall 12. The primary peripher y of the detector.

detector or plain mass ,1 is of conical shape and made from ebonite; the coil 6 is wound on the Figur'e5 shows a recording coil 1 to which 3 engraving a blank cylinder 4. The coil is pivoted at 5 to a soft iron armature 6 which is situated between the poles of an electromagnet7 energized by a coil 8. The currents sup lied tothe coil cause it to vibrate in anguler ashion about the axis 5 in a manner ver similar to the oscillation of a moving coll galvanometer. Flexible leads or mercury contacts convey the voice currents to the coil 1'. The mean depth of cut may be determined by a steady current in .thecoil, by a supplementary winding attached to and vibrating with the main winding, or by a spring control weak enough not to introduce an acoustic tone into the system, a .fine wire in torsion is very suitable. I I

Figures 6 and 7 show a circular coil 1' immersed in the field between the poles 9 and is attached a fin 2 carrying a recording jewel in the coil, a supplementary coil with a steady l phone 14 comprising an'insulating plate 15 i and two electrodes, one a ring 16 and the other a rod 17. Current for the microphone is supplied by the battery18. A non-inductive resistance 19 is inserted in the mircophone circuit. W'hen the jet ripples in response to vibrationthe resistance of the nappe or portion included between the electrodes 20 varies and therefore a corresponding change of potential occurs across the resistance 19 which variation of otential causesa-current to flow into the condenser 21 and through the resistance 22. The resistance 22 is sufiiciently small not seriously to disturb the condenser current. Again the variatioii of potential across the resistance 22 causes a-sr'naller current to flow into the condenser 23 which in turn causes minute variations of potential across the resistance 24; this latter variation is highly magnified by the relay 25 and converted into electric currents to operate the recording coil the frequency for the purpose of overcoming the resistance of the wax b ank to impression. Figure 9 illustrates another aspect of the Toavoid using a large number of turns I I onthis coil the current is transformed by the invention; here it is desired to record sound in the form of alateral cut on a disc blank 28 from the vibration of the plain mass 29 freely suspended by ligaments as at 30 due the direct action of the sound on the said mass when obstructing the aperture in the massive wall 31. A coil 32 is vibrated by the mass 29 between the poles 33 and 34 of an electromagnet. In this example the variations which are necessarily feeble are in the first place magnified by the valve relay 37 comprising theusual elements,namely, a filament 38, a grid 39, a plate 40 and, say, an inductance 41. In practice probably six valves in cascade would be required in place of the single valve 37 but the diagram has not been complicated by' the illustration of a multiplicity of valves or by the filament batteries. The electrical effects having been amplified by the relay 37 are then caused to operate the relay 42, in the plate circuit of which is placed a small inductance 43. The variation of potential across the inductance 43 is in turn amplified by the valve 44 in whose plate circuit is also placed a small inductance 45. It will be understood that the figure is diagrammatic only. Filament and high voltage batteries are omitted, according to common convention; also intervalve transformers in their complete form, all these being matters of ordinary practice and well understood. Valves 46 and 47 similar to valve 37 augment the current sufficientlyto provide the relatively large electromechanical forces required to vibrate the recording element 1 shown pivoted about the axis 13 and immersed in the field between the poles 9 and 10 of an electro-magnet. The stylus 3 is shown in process of engraving the disc. Assuming the resistance to the motion of the coil due to the engagement of the cutterwith the wax to be proportional to the instantaneous velocity of the cutter a fraction of the current which is the first diiferential of the true acoustic electric potential may be magnified and supplied to the coil without further differentiation for the purpose of compensating for this resistance. The diagram has not been complicated by the addition of this refinement which is within the competence of any one versed in the art to supply. v

Figure 10 is a view of a primary detector constructed according to the invention. In the annular space between the poles 33 and 34 of a powerful electromagnet is located the detecting coil 29, 32, mounted on the tissue pa-.

- comes practically nothing as in Dr. Drysdales per or indiarubber membrane 49. As a refinement a similar or approximately similar coil 50 is mounted on the ebonite ring 51 perforated with holes 52. Thecoils 29, 32 and50, are connected in series or parallel in such manner that the inductance of the two coils bewattm'eter (see Alternating Currents- Hay, 1907). The coil, however, only has to supply the grid current and as that is usually very small indeed the compensating coil 1s not essential. Sound is produced on the side of the wooden wall 31 remote from the magdisplacement wave of the incident sound."

This E. MI F. is brought to the terminals 35 and 36.

Figure 11 is ,a diagram illustrating the principle of the invention as applied to a mechanical engraving system possessing as near as may be one tone and applied to a mechanism of the Bell receiver class adapted to the case. The figure is in diagram only, filament and high voltage batteries being omitted to avoid complication. A detector with sensitive element 29, 32, controls the valve 42 in the plate circuit of which is placed an inductance 43 with iron core 53 and secondary winding 54 which transfers the potential variations with or without alteration of scale as circumstances allow to the valve 44 in the plate circuit of which is placed an inductance 45, a resistance 55 and erates the coil 58 of the electromagnetic engravinlg instrument through the transformer e engraving instrument comprises a permanent magnet 60 of the horse shoe type with laminated poles 61 and laminated armature 62 shaped so as to be as free as possible from tones likely to interfere with the recording and constrained by two wires 63 separated by the width of the armature and by the rubber pad 64 to which'one end is cemented. The magnet is carried by the ebonite bracket 65 pivoted at 66 to'a feedscrew carriagenot shown and counterbalanced to secure the proper gravitational pressure on the stylus 3, shown engraving the disc 28. An adjustmentblock 67 elastically hinged at 68 permits the distance of the armaturefrom the poles to be varied. It-is robe understood that the wires 63 are stretched by the magnetic force and that the natural period is largely determined by these wires. For the system to be practicable it is necessary for it to have a frequency of the order of one thousand cycles a second though the best pitch is a matter for experiment and varies according to the proportion adopted, At this natural frequency the electrical system 45, 55 and 56, only allows the transformer 57 to supply the damping losses.

Conceivably if thefarmature were a diaphragm with N tones in an important acoustic region'N systems in N valve transformers corresponding to 45, 55 and 56, or' possibly in parallel could be incor orated in the scheme. Again if inplace o the magnet and armature an engraving device as in Figures ratus engraving a cylindrical blank.

too thick or too thin by a separate'wire. A

cutting stylus 3 is attached to the coil. At Figure 12 is shown an elevation of the appa- Thewire 69 is knotted or otherwise enlarged at 70 so that the screwed ebonite brushes .71 situated in the ebonitelever 65 pivoted at 66 can be used to tension the wire 69 and cause it to press tightly against the rubber pads 72 cemented to the lever 65. A counterbalancing adjustment is provided at 73. Figure- 13 is an inverted plan of the apparatus in position between, the poles 9 and 10 of an electromagnet. A- plan from above is di- Jicted ,at. Figure 14. Wires' from the end 0 of the coil lead to the mercury pools 74 and 75 into which the distorted telephone currents are led bytheconductors76 and 77.

' Figure 15 is a greatly enlarged transverse sectional view of a recording coil for recording on a disc blank 28. The coil is situated in the magnetic air gap between the poles 9 and 10 of a powerful elect-romagnet. The field strength would be about 15000'c. g. s. units. To strengthen thecoil' the turns of which are bonded together with shellac or other binding material the central space is in part blocked in with wood or pitch 78. A

central fin 79 carries. the V-shaped ,recording jewel 3. If the effective length of the I winding is 400 cms. and the maximum transformed current is 1 ampere, the force on the coil' is approximately 300 grammes on each side.

applied to =1 sound'recording system it is obvious that the invention is equally appli-v cable to systems for reproducing sound, and wherever I have referred in the claims to a system of the class described, I have intended to include both sound recording and reproducing 'systems'as my system may reproduce sound by the substitution of a sound reproducer for the recorder element.

Divisible subject matter not claimed in is claimed in my copending applications Serial No. 30,605, filed May 15,1925, entitled Means for recording sound, and application Serial No. 284,587, filed June 11, 1928,-

ehtitledfReproduction ofsound; in my Letters Patent No. 1,639,713, dated August 23, 1927, entitled Reproduction of sound;

and in my application Serial No. 319,2 9, November 14,j1928,.for Reproduction o fbound.

Wha-t I claim is I I '1, 'In a system of the class describemaihon hereresonant primary detector, means for obtaining a potentlal from that detector and .meansfor obtaining a potential corresponding to the first, second or a higher differential of the potential derived from the detector.

2. In a system of the class described, a nonresonant primary detector and valve circuits arranged to yield potentials or currents.

Whichrepresent the first, second or higher diffeiyentials of. the potential or current yielded by the detector.

3. In a system ofthe class described, a nonresonant primary detector in combination with a thermionic valve in the plate circuit of which is placed an inductive-device the impedance of which is small compared with the impedance acoustic frequencies.

4. In a system of the class described, a nonresonant primary detector incombination of the valve for important a with a thermionic valve in the platecircuit of-which is placed a transformer the effec.- v tive lnductive impedance of which is small compared with the' plate circuit impedance for all important acoustic frequencies.

'5. In a system of the class described,-a non resonantprimary detector and two valve circuits connected by transformers whose inductive impedance is small compared with" that of the several plate circuits.

6. In a system of the class described,a non- I resonant primary detector and a valvecircuit-capable of producin from the detector a mixture of the original potential and one or more differentials in desired proportions.

7. In a system of the class described, a material body free from natural frequencies over the important acoustic range, a winding arranged to move with the said body and'supported in such a way as to constitute a plain engaging with the winding and one or more valvecircuits adapted to modify the elec- 8. In a system of the class described, a Inaterial body free from natural frequencies I .mass means for roducin a ma netic field While I have dGSQI'lbGCl my invention as p D g overthe important acoustic range, a-wind- "ing arranged to move with the said body and supported in such a way asto constitute a plain mass, means for producing a magnetic field engaging with the winding and means for obtaining a potential which is the first,

second or higher differential of the electrical effect due to the movements of the winding.

9. In system of the class described, the combination of microphonic means comprising a sound 1'esponsive-body'fr'e from natural tones within the important acoustic range and freely supported, detecting means for obtaining electric potentials-which vary with r the movement of-said with a thermionic relay having-inits circuit means arranged to increase the potentials obtained from the said detecting means in proportion to the frequencies of the said potentials. 10. In means for recording sound the combination of a primary detector which is itself intrinsically non-resonant, means for obtaining an electric potential which varies with the movements of the detector due to the inf cidence of sound waves, means for producing current controlled by said potential and an 10 electro-inech anical recording device characterized, in that the moving part or arts thereof have no elastic restraint capab e of imparting resonant properties to the said part or parts, which recording device is 1 adapted to be operated by said currents. I

11. In means for recording sound, the combination of a non-resonant primary detector itself intrinsically non-resonant and which constitutes a plain mass, means for obtaining an'electric potential which varies with the movements of the detector "due to .the incidence of sound waves, means for producing currents controlled by said potential and an electro-mechanical engraving device characterized, in that the moving part or arts thereof have no elastic restramt capab e of imparting resonant ropertiesto the said part or parts, which engraving device ,is adapted to be 0 erated by said currents.

12. In means or recordmg sound, the com"-' bination of a substantially non-resonant detector 'for soundi'waves, means for (producing an electric potential varying accor ing to the sound waves, and a recording device comprising a compact vibrating element free from external control and friction and determining substantially by mass alone the amplitude of its'vibration due to an electromagnetic impulse supplied from said non-resonant detector. l I a 13. In means for recording sound, the com- 4 bination of a substantially non-resonant detector means for producing an electric potential varying according to the sound waves, means for distorting the variations of potential to produce avarying current, and a recording device comprising a compact vibrating element free from external control and friction and determining substantiallyby mass alone the amplitude of its vibration due to. an electromagneticgimpulse supplied from said non-resonant detector.

14. In means for recording sound, the combination of means for producing an electric potential varying according to the sound waves, means for distorting the variations of potential so that every harmonic is enlarged in proportion of the square of its frequency rto produce a varying current, and a record- 6 ing device comprising a compact vibrating element free from external control and friction and determining substantially by mass alone the amplitude of its vibration'due to an electromagnetic impulse.

bination of means in itself non-resonant for resonant connected. to the other" side of the relay and immersed in a magnetic field and an engraving stylus carried by the coil.

16. In means for recording sound, the com: bination of means in itself non-resonant for obtaining an electric potential from sound waves, and an electro-mechanical recording device comprising an element having no elastic restraint capable of imparting resonant properties to said element and means for supporting said element for-vibration about an axis.

17. In means for recording sound, the com-;

obtaining an electric potential from sound waves, and an electro-magnetic recording device comprising a. mechanical vibratory clementhaving no elastic restraint capable of imparting resonant properties to said element and means for supporting'said element for torsional vibration.

18. In means for recording sound, the com-. bination of means in itself non-resonant for obtaining an electric potential from sound waves and an electro-magnetic recording device comprising a vibratory element which is non-resonant, a floating beam, and means for supporting said element from said beam for torsional vibration.

19. In means for recording sound, the combination of means in itself non-resonant for obtaining an electric potential from sound waves, an electro-Inagnetic recording device which is in effect non-resonant and substantially free from static friction and is adapted to cut a sound groove in a wax blank and means for regulating the depth of cut in the wax.

20. In means for recording sound, the combinationlof means for obtaining an electric potential from sound waves, including a conducting sheet in effect non-resonant, means for producing a magnetic field, a plurality of valve circuits, transformers which couple these circuits "and the inductive impedance conductin recordin element immersed in a magnetic eld and a apted to-en rave a trace.

of its-vibration on a record blan 22. In means for recording sound, the combination of means for obtaining an electric potential from sound waves, including a conducting sheet in effect non-resonant, meansfor produein a magnetic field, valve circuits for differentiating and integrating the potential derived from the conducting sheet in desired proportions, and an electro-mehanical substantially lion-resonant recording ple-.

ment adapted to engravea trace of its vibration on a wax blank.

23. In means for recording sound, the combination of means' for obtaining an electric sired proportions, and an electromechanical recording element in itself non-resonant adapted to en ave a trace of its vibrations on a wax blan l 24. A non-resonant detector including means whereby a potential is derived from sound waves, means for amplifying the said potential, means for integrating such potential, and a non-resonant recorder operated by such integrated potential.

25. In combination a non-resonant primar detector, an electrical system connected wit said detector for deriving a potential therefrom and means connected with said electrical system for obtaining a pluralit of differential potentials with respect tot e potential derived from the detector, and responsive means actuated by the differential potentials. In, testimony that I claim the foregoing as my invention I have signed my name this -29th'day of October 1920. v

' ADRIAN FRANCIS SYKES. 

